1. Field
An aspect of an embodiment of the present invention relates to an organic light emitting display device and a driving method thereof.
2. Description of Related Art
Various flat panel display devices with reduced weight and volume in comparison to a cathode ray tube have been developed. Examples of the flat panel display devices include a liquid crystal display device, a field emission display device, a plasma display panel, an organic light emitting display device, etc.
Among the flat panel display devices, the organic light emitting display device displays an image by using organic light emitting diodes that emit light by recombining holes with electrons. The organic light emitting display device has low power consumption while having rapid response speed.
FIG. 1 is a circuit diagram showing a pixel of an organic light emitting display device according the related art.
Referring to FIG. 1, a pixel 4 includes a pixel circuit 2 for controlling an organic light emitting diode (OLED) connected to the pixel circuit 2, a data line Dm, and a scan line Sn.
An anode electrode of the OLED is connected to the pixel circuit 2, and a cathode electrode of the OLED is connected to a second power supply ELVSS. The OLED generates light having a luminance (e.g., a predetermined luminance) corresponding to the amount of current supplied from the pixel circuit 2.
The pixel circuit 2 controls the amount of current supplied to the OLED to correspond to a data signal provided from the data line Dm when a scan signal is provided to the scan line Sn. Here, the pixel circuit 2 includes a second transistor M2 connected to a first power supply ELVDD and the OLED, a first transistor M1 connected to the second transistor M2, the data line Dm, and the scan line Sn, and a storage capacitor Cst connected between a gate electrode and a first electrode of the second transistor M2.
A gate electrode the first transistor M1 is connected to the scan line Sn, and the first electrode of the first transistor M1 is connected to the data line Dm. In addition, a second electrode of the first transistor M1 is connected to one terminal of the storage capacitor Cst. Here, the first electrode is one of a source electrode or a drain electrode, and the second electrode is an electrode other than the first electrode. For example, when the first electrode is the source electrode, the second electrode is a drain electrode. The first transistor M1 connected to the scan line Sn and the data line Dm is turned on and provides the data signal provided from the data line Dm to the storage capacitor Cst when a scan signal is provided from the scan line Sn. Here, the storage capacitor Cst is charged with a voltage corresponding to the data signal.
The gate electrode of the second transistor M2 is connected to one terminal of the storage capacitor Cst, and the first electrode of the second transistor M2 is connected to the other terminal of the storage capacitor Cst and the first power supply ELVDD. In addition, a second electrode of the second transistor M2 is connected to the anode electrode of the OLED. The second transistor M2 controls the amount of current that flows to the second power supply ELVSS via the OLED from the first power supply ELVDD to correspond to a voltage value stored in the storage capacitor Cst. Here, the OLED generates light corresponding to the amount of current supplied from the second transistor M2.
The pixel 4 supplies a current corresponding to the voltage charged in the storage capacitor Cst to the OLED to display an image having a luminance (e.g., a predetermined luminance). However, the above described organic light emitting display device cannot display an image having uniform luminance due to a variation in threshold voltage of the second transistor M2.
In the related art, additional circuits such as a plurality of transistors are included in the pixel 4 for compensating for the variation of the threshold voltage of the second transistor M2. However, when the plurality of transistors (for example, 6 transistors) are included in the pixel 4 in order to compensate for the variation of the threshold voltage of the second transistor M2, reliability is deteriorated.
Further, in the related art, a voltage value of the first power supply ELVDD varies due to a voltage drop depending on the position of the pixel 2, and as a result, an image having desired luminance cannot be displayed.